The present invention is directed to a print unit of an offset printing press. Components of the print unit are supported in frame modules which are separable. Size ratios exist between various ones of the components.
An offset printing press with two print units which are placed opposite each other is known from DE 198 33 468 A1. The print units each have two forme cylinders, two transfer cylinders and a counter-pressure cylinder. The print units which are placed opposite each other are seated in a frame consisting of two frame modules. By separating the frame modules, the print units can be arranged so their distance in relation to each other can be changed.
A webfed rotary printing press is known from EP 0 958 917 A1, whose printing group consists of two print units which are arranged opposite each other. The paper web to be imprinted can be conducted in a vertical center plane between the print units. Each of the individual print units has a forme cylinder, a transfer cylinder and an ink unit. The paper web is conducted between the transfer cylinders, which are arranged opposite each other, of two print units which are also arranged opposite each other in such a way that the opposing transfer cylinder operates in the manner of a counter-pressure cylinder. The individual printing groups, which are arranged on top of each other and each consisting of two print units, are seated in a frame in such a way that they can be displaced in the vertical direction so that their distance can be changed.
A multi-color web-fed rotary printing press is known from DE 44 29 891 A1, and whose print units each have a forme cylinder and a transfer cylinder. In this device, the transfer cylinder has twice the circumference of the forme cylinder. Two print units are arranged opposite each other in a frame which has three frame modules. The frame modules can be arranged so their distance from each other can be changed in such a way that the area between the individual forme cylinders and the oppositely located transfer cylinder is accessible to the operators.
EP 0 563 007 A1 and U.S. Pat. No. 2,557,381 both disclose how to arrange different cylinders in several separable frame modules.
DE-PS M 219 15XII./15d shows a printing group in which the forme and transfer cylinders have identical diameters, and the counter-pressure cylinder has twice the diameter of the forme and transfer cylinders.
A web-fed offset printing press is known from EP 0 352 521 A2, whose print units each have a forme cylinder, a transfer cylinder and utilize a common satellite cylinder, which operates in the manner of a counter-pressure cylinder. The circumference of the satellite cylinder corresponds to the circumference of the forme cylinder and to half the circumference of the transfer cylinder.
An offset printing group is known from DE 198 03 809 A1, whose print units have a forme cylinder, a transfer cylinder and a satellite cylinder, which is assigned to two transfer cylinders. The circumference of the transfer cylinder is twice the circumference of the forme cylinder, and the circumference of the satellite cylinder corresponds to the circumference of the transfer cylinder.
The object of the present invention is directed to providing a print unit for an offset printing press.
In accordance with the present invention, this object is attained by the provision of a plurality of print units which are arranged to form printing groups. These printing groups are each formed by oppositely arranged forme cylinders and transfer cylinders. The opposing print groups are supported in separable left and right frame modules. At least one counter-pressure cylinder is situated in a center module. The circumference of the counter-pressure cylinder is 1.5 times or twice the circumference of the transfer cylinder and a whole number multiple of the printed page height.
The advantages to be gained by the present invention consist, in particular, in that the frame for seating the cylinders of the offset printing press in a manner fixed on the frame is composed of three separable frame modules. The forme cylinders, transfer cylinders and ink units and, to the extent provided, other installations, such as, for example dampening units, of the left print units are seated in a left or first frame module. A right or second frame module correspondingly receives the forme cylinders, transfer cylinders and ink units of the right print units. A center or intermediate frame module is provided between the left and right, or first and second frame modules. The counter-pressure cylinders, which act together with the transfer cylinders when the web of material, for example a paper web, is imprinted, are seated in this center or intermediate frame module. By separating and moving the individual frame modules away from each other, the print units can be opened such that the oppositely located counter-pressure cylinders on the center frame module, as well as the forme and transfer cylinders on the right or left frame module, are simultaneously accessible.
The frame modules can be displaced in a direction extending radially in respect to the axes of rotation of the cylinders. Alternatively or coincidentally, the modules can be moved in an axis-parallel direction in respect to the axes of rotation of the cylinders.
A further advantage to be gained by the present invention consists, in particular, in that the circumference of the counter-pressure cylinder corresponds to 1.5 times or to twice the circumference of the transfer cylinder. Furthermore, the circumference of the counter-pressure cylinder must, at the same time, correspond to a whole number multiple of the height of a printed page, taken in the circumferential direction of the forme cylinder. As a result of this, extraordinarily rigid counter-pressure cylinders are created, which do not exceed permissible deformation tolerances even under the highest stress. Moreover, a good support effect in respect to the other cylinders of the print units is also achieved.
Selecting the circumference of the counter-pressure cylinder to correspond to 1.5 times or to twice the circumference of the transfer cylinder is particularly advantageous if, in the course of imprinting a web of material, a counter-pressure cylinder cooperates, in the manner of a satellite cylinder, with respectively two transfer cylinders, which are arranged on top of each other, of two print units. Thus, particularly compact structures result from using the circumference ratios when installing the cylinders in the frame of an offset printing press.
If the circumference of the forme cylinder substantially corresponds to the height of a printed page, and in particular to the height of a newspaper page, so that if one printed side can be imprinted during one revolution of the forme cylinder, it is particularly advantageous for the support of the forme cylinder to select a transfer cylinder with twice the circumference of the forme cylinder. Because of this, the forme cylinder is supported by the substantially more rigid transfer cylinder in an advantageous manner. In accordance with a preferred embodiment of the present invention, with this circumferential ratio between the forme cylinder and the transfer cylinder, the circumference of the counter-pressure cylinder can be designed to be 1.5 times the circumference of the transfer cylinder. With this constellation, the result is that the circumference of the counter-pressure cylinder substantially corresponds to three times, and thus to a whole number multiple, of the height of the printed page.
In accordance with a further preferred embodiment of the present invention, the circumference of the forme cylinder substantially corresponds to twice the height of a printed page, so that two printed pages can be printed during one revolution of the forme cylinder. In this embodiment, the circumference of the transfer cylinder is selected to correspond to the circumference of the forme cylinder, and the circumference of the counter-pressure cylinder again corresponds to 1.5 times the circumference of the transfer cylinder. With this constellation of cylinder circumferences, the result also is that the circumference of the counter-pressure cylinder substantially corresponds to three times, i.e. a whole number multiple, of the height of a printed page.
In accordance with yet a further preferred embodiment, the circumference of the forme cylinder substantially corresponds to the height of a printed page, and the circumference of the transfer cylinder is selected to correspond to the circumference of the forme cylinder. To achieve advantageous relationships between the cylinder circumferences in this embodiment, the circumference of the counter-pressure cylinder is selected to be twice the circumference of the transfer cylinder. The circumference of the counter-pressure cylinder now substantially corresponds to twice, and thus to a whole number multiple, of the height of a printed page.